I'm thinking about doing a large amount of ribs but I only have 2 rib racks (3 racks per). Does anybody have any suggestions on how to rig up or improvise something to fill the bill for a one time deal or am I better to just invest in more racks?

I don't really want to cook them in advance because they're never quite as good.

Its MacGyver time. Here we go...
1) Set up a line of bricks at each end of the pit.
2) Use thin strands of metal (hangers) lined up horizontally about two inches apart on top of the bricks.
3) Cap with another line of bricks.
4) Insert ribs between hangers.

OK - I must admit that I have never tried rib racks before. When I make ribs I make them on my smoker - I always assumed that the rib racks helped those who did not have a smoker and simply fixed ribs on a grill, am I wrong about that? If anyone uses these with a smoker what is the benefit. Sorry about the basics here it is something that I just never looked into or tried.

I like the ones that are wire built over the ones that are sheet metal built. I like the fact that I can see the racks easier over some of the ones that are more closed in. There are many on the market. I bought mine at Lowes. Its nice because it also has potato spikes on the edges.
Let me poke around the net and see if I can find a link for you to one or two.